UPDATE: New album with additional photos here: https://i.stack.imgur.com/8yGX2.jpg

My parent's house has a pretty bad leak that has been going for a few years. Because of money and other issues with the house I need to try do an improvement myself if at all possible. Getting a new roof (or house, since everything else is outdated/has an issue) may be possible down the line but not right now.

One thing slightly in my favor is this is in San Diego so it rains infrequently.

I have included some pictures. In the last you can see where I pulled some of the ceiling down where it was mostly soft/mushy. Asbestos test was negative.

Estimators have suggested the issue is definitely with the valley and one of them recommended I could install flashing in/along/under (not sure what he meant) the valley to improve the situation. I purchased a roll of aluminum flashing. I am not clear on exactly where to put it though.

The examples I see on youtube when I search 'roof valley' don't have such a low slope or the part where it goes up/horizontally again like that. The ones I saw were mostly just one smooth seem. If it was like that then I have some tutorials on doing underlayment, flashing, trimming shingles for a normal valley. But I haven't seen an example quite like my roof.

Thanks so much for any advice.

roof roof 2

roof 3


  • Flashing goes under the shingles, in the old days you had a metal valley with the shingles seperated by several inches. today it is normal to have a valley like you have. you will want to start above the leak point if just a repair.
    – Ed Beal
    Jan 19, 2016 at 23:50
  • The shingles actually don't look so bad. I don't see any damaged or missing. Since the ceiling is open pinpoint the water entry point and remove the shingles from that area and roof patch the hell out of it. Return the shingles when done.
    – ojait
    Jan 19, 2016 at 23:52
  • The roof blocks held a tarp in place? That sky light could be the leak source?
    – ojait
    Jan 19, 2016 at 23:54
  • @ojait Yes I was using those blocks to hold a tarp. A few people have been suspicious of the skylight but they seem to think the valley is more likely. One said there was a depression where it looked to be able to pool up at a point in the valley. Jan 19, 2016 at 23:59
  • @JasonLivesay - I'd put money on the problem being where the valley intersects with the eave. There's an awkward intersection there where it's usually pretty difficult to get the valley flashing (or likely under-layment in this case) completely integrated with step flashing and shingles underneath the eave. Without re-doing the intersection (which would mean quite a bit of tear-off), your best bet is likely going to be running tar down the valley seam.
    – Comintern
    Jan 20, 2016 at 0:35

2 Answers 2


Yeah, that roof's pretty beat. I'd actually go heavily at that seam with Mortar Caulk (its gritty & gray), the whole length of the seam if you don't know where the leak is. But, spraying a hose at the seam & very slowly moving the spray up the seam should give you a good idea of the problem area.

Still caulk the whole seam, but then do under the shingles in the leak zone. Be careful & don't pry them anymore if they're brittle & chunks start snapping off. I caulked a flat roof in the rain 3-years ago & it still hasn't let in a drop.

  • Mortar Caulk, didn't know that was an option, thanks. Jan 20, 2016 at 0:17
  • No problem. It's worth a shot & really shouldn't be noticed at all. Maybe 2 tubes of it & it's good for any brick, stone or concrete mortar sealing. I hope it does the trick & hopefully the seam's the problem.
    – Iggy
    Jan 20, 2016 at 0:25
  • just to double check, you mention brick/stone/concrete.. this is wood in some places and mostly asphalt shingles of course.. the mortar caulk still applies to shingles right? Jan 20, 2016 at 1:07
  • Oh yeah! I was just meaning, if you have any left over you can use it anywhere else around the house. By the by, you may want 2 coats. The first application being to squirt it actually into the seam & another to smooth over with your figure or to even draw lines in it to blend it into the shingle rows.
    – Iggy
    Jan 20, 2016 at 1:14

Low sloped roofs are problematic only when they get wet! (the water doesn't shed fast enough). What the roof contractor probably meant regarding flashing the valley was (I'm guessing) is if you re-roof it would install under the new shingles.

Here is an easier and more successful suggestion which I have used with great results. If you'd rather defer a new roof installation, but need a repair to last for several years substitute the metal valley flashing with a section of rolled roofing. Made from the same material as asphalt shingles rolled roofing is actually best used for roofs with low slopes. It is sold in 3' x 90' (?) rolls and can be cut to any length. Roof nails and rolled roofing lap cement secure and bond each section.

Cut a length to cover the leaking roof valley. Do this if possible so the sun can soften the rolled roofing before installation. position the rolled roofing section centered on the valley. At the top fold it down to expose 24 inches of the shingled roof and apply lap cement on the old shingles. Press the roofing into cement and nail the top edge and 24 inches down the sides (space nails 3-4 inches).

Flap back one side and apply cement and nail. Repeat on the other side and bottom. Dab the nail heads with cement to finish repair.

  • OK thank you for the idea. The other side of that low slope roof has had the shingles replaced with rolled roofing several years ago because of a different leak. Jan 20, 2016 at 0:01
  • Just so I can make sure I understand how to position the rolled roofing, I should essentially unroll it down the length of the valley, so there will be about 18 inches of rolled roof on either side of the valley? Then the nails will go in on top of the rolled roof, into the shingles below, and sealed with roofing cement? Jan 20, 2016 at 0:06
  • Yes. Exactly. But be sure that the source of the leak is being covered by the rolled roofing. If possible, locate it through the opened ceiling. If you are unsure install three sections down the valley: one down the middle and the other two lapped on top and on either side of the middle one by 4-8 inches. Use 2" roof nails and brush the lap cement liberally on the tabbed shingles.
    – ojait
    Jan 20, 2016 at 0:29
  • Actually, as far as valleys go, lower pitch is usually less problematic because the cross-wash angle gets smaller as the pitch gets lower.
    – Comintern
    Jan 20, 2016 at 0:30
  • Not sure how the edges of rolled roofing will seal against the dimensional shingles running perpendicular... maybe with a crap load of tar? Maybe use some torch-down stuff? Jan 20, 2016 at 5:25

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